<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="https://cdn.bootcdn.net/ajax/libs/vue/2.6.12/vue.js"></script>
</head>
<body>
    <div id="app"></div>
    <script>
        <!--  1.Vue是一个构造函数 -->
        // console.log(Vue)
        // ƒ Vue (options) {
        //     if (!(this instanceof Vue)
        //     ) {
        //         warn('Vue is a constructor and should be called with the `new` keyword');
        //     }
        //     this._init(options);
        // }
    </script>
</body>
</html>